Field of the Invention
This invention relates to apparatus for the warming of liquid to a desired temperature. Specifically, in surgical operations, it is often desired to have a quantity of sterile solution available which is maintained at body temperature. Historically, this need has been addressed in a number of ways.
In a "passive" approach, a large cast-iron base for a heating element was provided on a standard open basin. The heating element was in contact with the bottom of the basin and with some portion of the side of the basin as well. A sterile drape was used to quarantine the heating element from the sterile basin. However, this approach suffered from a number of drawbacks. Because there was no way to ensure consistent thermal contact with the heating element, uneven heating and "hot spots" would develop. Secondly, because the boundary between the basin and the heater was not thermally efficient, the heating element had to be maintained at quite a high temperature if rapid warming was desired. This caused the heating element to become dangerously hot to the touch, and also resulted in significant overshooting of the target solution temperature. This approach also suffered from unpredictable temperature gradients within the solution and varying heating characteristics depending upon the amount of solution in the basin. A second passive approach involved a thin film heater assembly, specifically a simple circular "spot" heater located at the center of a standard basin. However, because the source of heat was relatively confined, the solution was warmed too slowly, produced unacceptably high temperatures on the basin bottom, and produced undesirable solution temperature gradients during operation.
An "active mixing" approach was attempted in order to solve the control difficulties of the passive approaches. The active approach employed a pump to recirculate the solution from the basin, to an external heater, and back into the basin. While this approach did solve many of the problems inherent in the passive approaches, it was quite a bit more expensive and was found to generate a great deal of noise in the operating room. An alteration of this approach employed an air bubbler system to achieve a uniform temperature in the solution.